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(1) Field of the Invention
This invention relates to a polyurethane-forming no-bake foundry binder comprising a (a) polyether polyol component comprising (1) a polyether polyol, (2) hydrofluoric acid, and (3) an aminoalkoxysilane, (b) a polyisocyanate component, (c) a liquid tertiary amine catalyst component. Foundry mixes are prepared by mixing the binder system with a foundry aggregate by a no-bake process. The resulting foundry shapes are used to cast metal parts from ferrous and non-ferrous metals.
(2) Description of the Related Art
One of the major processes used in the foundry industry for making metal parts is sand casting. In sand casting, disposable foundry shapes (usually characterized as molds and cores) are made by shaping and curing a foundry binder system that is a mixture of sand and an organic or inorganic binder. The binder is used to strengthen the molds and cores.
Two of the major processes used in sand casting for making molds and cores are the no-bake process and the cold-box process. In the no-bake process, a liquid curing agent is mixed with an aggregate and binder, and shaped to produce a cured mold and/or core. In the cold-box process, a gaseous curing agent is passed through a compacted shaped mix to produce a cured mold and/or core. Phenolic urethane binders, cured with a gaseous tertiary amine catalyst, are often used in the cold-box process to hold shaped foundry aggregate together as a mold or core. See for example U.S. Pat. No. 3,409,579. The phenolic urethane binder system usually consists of a phenolic resin component and polyisocyanate component which are mixed with sand prior to compacting and curing to form a foundry binder system. Because the foundry mix often sits unused for extended lengths of time, the binder used to prepare the foundry mix must not adversely affect the benchlife of the foundry mix.
Among other things, the binder must have a low viscosity, be gel-free, remain stable under use conditions, and cure efficiently. The cores and molds made with the binders must have adequate tensile strengths under normal and humid conditions, and release effectively from the pattern. Binders, which meet all of these requirements, are not easy to develop.
Because the cores and molds are often exposed to high temperatures and humid conditions, it also desirable that the foundry binders provide cores and molds that have a high degree of humidity resistance. This is particular important for foundry applications, where the core or mold is exposed to high humidity conditions, e.g. during hot and humid weather, or where the core or mold is subjected to an aqueous core-wash or mold coating application for improved casting quality.
Phenolic urethane cold-box and no-bake foundry binders often contain a silane coupling agent and/or aqueous hydrofluoric acid to improve humidity resistance. See for example U.S. Pat. No. 6,017,978. Although this patent covers the use of silanes in general, the examples utilize a ureido silane, which is preferred. The silane and hydrofluoric acid are typically added to the phenolic resin component of the binder.
However, a disadvantage of adding the silane and free aqueous hydrofluoric acid to phenolic urethane no-bake binders, is that the addition retards the chemical reaction, and thus increases the worktime of the foundry mix and the striptime of the core or mold. If a longer time is required for the sand mix to set, this negatively affects productivity.
All citations referred to under this description of the xe2x80x9cRelated Artxe2x80x9d and in the xe2x80x9cDetailed Description of the Inventionxe2x80x9d are expressly incorporated by reference.
This invention relates to a polyurethane-forming no-bake binder comprising:
(a) a polyether polyol component comprising,
(1) a polyether polyol,
(2) a fluorinated acid, and
(3) an aminoalkoxysilane,
(b) a polyisocyanate component, and
(c) a liquid amine curing catalyst.
Cores and molds made with the binders have excellent humidity resistance, and this is achieved without substantial adverse effects on the reactivity of the binder, i.e. the worktime of the foundry mix and the striptime of the core or mold from the pattern is not substantially increased. Thus, the use of these binders have an advantage not found when phenolic urethane having similar formulations are used as no-bake binders, since the worktime of foundry mixes made with phenolic urethane binders typically increases and the striptime also increases, when hydrofluoric acid and a silane are added to the binder. This improvement is significant because, if a longer time is required for the sand mix to set, this adversely affects productivity. These advantages are obtained without sacrificing other properties such as casting quality.
The invention also relates to the use of the binders in foundry mixes, core-making by the no-bake process, and in the casting of ferrous and non-ferrous metals.
Not Applicable.
The detailed description and examples will illustrate specific embodiments of the invention will enable one skilled in the art to practice the invention, including the best mode. It is contemplated that many equivalent embodiments of the invention will be operable besides these specifically disclosed.
The aminoalkoxysilanes used in the binder composition typically have the following general formula: 
wherein:
(1) R1 and R2 are selected from the group consisting of H; alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups; di- or triamino groups, amino alkyl groups, amino aryl groups, amino groups having mixed alky-aryl groups, and amino groups having substituted alkyl groups, aryl groups, mixed alky-aryl groups; and alkoxysilane groups, where R1 and R2 can be the same or different and preferably where at least one of the R1 and R2 groups is H, and the other group is an unsubstituted alkyl group having 1-4 carbon atoms;
(2) n is a whole number from 1 to 3, preferably where nxe2x89xa71;
(3) n+m=3;
(4) p is a whole number from 1 to 5, preferably 2 to 3, and
(5) Ra and Rb are selected from the group consisting of alkyl groups, aryl groups, mixed alky-aryl groups, substituted alkyl groups, aryl groups, preferably an unsubstituted alkyl group having from 1-carbon atoms, and can be identical or different.
This structure does not include ureido silanes, which do not work effectively for purposes of this invention.
Specific examples of aminoalkoxysilanes include 3-aminopropyldimethyl-methoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyl-triethoxysilane, 3-aminopropylmethyl-dimethoxysilane 3-aminopropylmethyl-diethoxysilane, N-(n-butyl)-3-aminopropyl-trimethoxysilane, N-aminoethyl-3-aminopropylmethyl-dimethoxysilane, 3-ureidopropyltrimethoxysilane, 3-ureido-propyltriethoxysilane, N-phenyl-3-aminopropyl-trimethoxysilane, N-[(Nxe2x80x2-2-aminoethyl)-2-aminoethyl)]-3-aminopropyltrimethoxysilane and bis (3-trimethoxy-silylpropyl) amine. Preferably used as the aminoalkoxysilanes are aminoalkoxysilanes where R1 and R2 are selected from the group consisting of H; alkyl groups, aryl groups, substituted alkyl groups, aryl groups, mixed alky-aryl groups; di- or triamino groups, amino alkyl groups, amino aryl groups, amino groups having mixed alky-aryl groups, and amino groups having substituted alkyl groups, aryl groups, mixed alky-aryl groups; and alkylsilanol groups, preferably where at least one of the R1 and R2 groups is H and the other group is an unsubstituted alkyl group having 1-4 carbon atoms.
The polyether polyol component comprises a polyether polyol. The polyether polyols, which are used in the polyurethane-forming foundry binders are liquid polyether polyols or blends of liquid polyether polyols typically having a hydroxyl number of from about 200 to about 1000, preferably about 300 to about 800 milligrams of KOH based upon one gram of polyether polyol. The viscosity of the polyether polyol is typically from 100 to 1000, centipoise, preferably from 200 to 700 centipoise, most preferably 250 to 600 centipoise. The polyether polyols may have primary and/or secondary hydroxyl groups.
These polyols are commercially available and their method of preparation and determining their hydroxyl value is well known. The polyether polyols are prepared by reacting an alkylene oxide with a polyhydric alcohol in the presence of an appropriate catalyst such as sodium methoxide according to methods well known in the art. Any suitable alkylene oxide or mixtures of alkylene oxides may be reacted with the polyhydric alcohol to prepare the polyether polyols. The alkylene oxides used to prepare the polyether polyols typically have from two to six carbon atoms. Representative examples include ethylene oxide, propylene oxide, butylene oxide, amylone oxide, styrene oxide, or mixtures thereof. The polyhydric alcohols typically used to prepare the polyether polyols generally have a functionality greater than 2.0, preferably from 2.5 to 5.0, most preferably from 2.5 to 4.5. Examples include ethylene glycol, diethylene glycol, propylene glycol, trimethylol propane, and glycerine.
Although not necessarily preferred or required, the polyether polyol component may contain solvents.
The polyether polyol component may also contain other polyols, particularly aliphatic, and/or preferably aromatic polyester polyols. The aromatic polyester polyols, or a blend of liquid aromatic polyester polyols, typically have a hydroxyl number from about 200 to 2,000, preferably from 200 to 1200, and most preferably from 250 to 800; a functionality equal to or greater than 2.0, preferably from 2 to 4; and a viscosity of 500 to 50,000 centipoise at 25xc2x0 C., preferably 1,000 to 35,000, and most preferably 1,500 to 25,000 centipoise. They are typically prepared by ester interchange of aromatic ester and alcohols or glycols by an acidic catalyst. The amount of the aromatic polyester polyol in the polyol component is typically from 2 to 65 weight percent, preferably from 10 to 50 weight percent, most preferably from 10 to 40 weight percent based upon the polyol component. Examples of aromatic esters used to prepare the aromatic polyesters include phthalic anhydride and polyethylene terephthalate. Examples of alcohols used to prepare the aromatic polyesters are ethylene glycol, diethylene glycol, triethylene glycol, 1,3-propane diol, 1,4-butane diol, dipropylene glycol, tripropylene glycol, tetraethylene glycol, glycerin, and mixtures thereof. Examples of commercially available aromatic polyester polyols are STEPANPOL polyols manufactured by Stepan Company, TERATE polyol manufactured by KOSA, THANOL aromatic polyol manufactured by Eastman Chemical, and TEROL polyols manufactured by Oxide Inc.
Although not necessarily preferred, phenolic resins, e.g. novolac resins and phenolic resole resins, and/or amine-based polyols can be added to the polyol component. If a phenolic resin is added to the polyether polyol, the preferred phenolic resins used are benzylic ether phenolic resins which are specifically described in U.S. Pat. No. 3,485,797 which is hereby incorporated by reference into this disclosure.
The polyisocyanate component of the binder typically comprises a polyisocyanate and organic solvent. The polyisocyanate has a functionality of two or more, preferably 2 to 5. It may be aliphatic, cycloaliphatic, aromatic, or a hybrid polyisocyanate. Mixtures of such polyisocyanates may be used. Also, it is contemplated that chemically modified polyisocyanates, prepolymers of polyisocyanates, and quasi prepolymers of polyisocyanates can be used. Optional ingredients such as release agents may also be used in the polyisocyanate hardener component.
Representative examples of polyisocyanates which can be used are aliphatic polyisocyanates such as hexamethylene diisocyanate, alicyclic polyisocyanates such as 4,4xe2x80x2-dicyclohexylmethane diisocyanate, and aromatic polyisocyanates such as 2,4xe2x80x2- and 2,6-toluene diisocyanate, diphenylmethane diisocyanate, and dimethyl derivatives thereof. Other examples of suitable polyisocyanates are 1,5-naphthalene diisocyanate, triphenylmethane triisocyanate, xylylene diisocyanate, and the methyl derivatives thereof, polymethylenepolyphenyl isocyanates, chlorophenylene-2,4-diisocyanate, and the like.
The polyisocyanates are used in sufficient concentrations to cause the curing of the phenolic resin when catalyzed with the tertiary amine curing catalyst. In general the isocyanato group ratio of the polyisocyanate component to the hydroxyl groups of the polyether polyol component is from 1.25:1 to 1:1.25, preferably about 1:1. The polyisocyanate is used in a liquid form. Solid or viscous polyisocyanates must be used in the form of organic solvent solutions. In general, the solvent concentration will be in the range of up to 80% by weight of the resin solution and preferably in the range of 20% to 80%.
Those skilled in the art will know how to select specific solvents for the polyisocyanate component. Non polar solvents, e.g. aromatic solvents, are useful because they are compatible with the polyisocyanate. Examples of aromatic solvents include xylene and ethylbenzene. The aromatic solvents are preferably a mixture of aromatic solvents that have a boiling point range of 125xc2x0 C. to 250xc2x0 C.
The solvent component can include drying oils such as disclosed in U.S. Pat. No. 4,268,425. Such drying oils include glycerides of fatty acids which contain two or more double bonds. Also, esters of ethylenically unsaturated fatty acids such as tall oil esters of polyhydric alcohols or monohydric alcohols can be employed as the drying oil. In addition, the binder may include liquid dialkyl esters such as dialkyl phthalate of the type disclosed in U.S. Pat. No. 3,905,934 such as dimethyl glutarate, dimethyl adipate, dimethyl succinate; and mixtures of such esters.
Although not required when the aminoalkoxysilanes of this invention, the binder may also contain a silane (typically added to the polyol component) having the following general formula: 
wherein Rxe2x80x2, Rxe2x80x3 and Rxe2x80x2xe2x80x3 are hydrocarbon radicals and preferably an alkyl radical of 1 to 6 carbon atoms and R is an alkyl radical, an alkoxy-substituted alkyl radical, and can be identical or different. The silane is preferably added to the phenolic resin component in amounts of 0.01 to 5 weight percent, preferably 0.1 to 1.0 weight percent based on the weight of the phenolic resin component.
When preparing an ordinary sand-type foundry shape, the aggregate employed has a particle size large enough to provide sufficient porosity in the foundry shape to permit escape of volatiles from the shape during the casting operation. The term xe2x80x9cordinary sand-type foundry shapes,xe2x80x9d as used herein, refers to foundry shapes which have sufficient porosity to permit escape of volatiles from it during the casting operation.
The preferred aggregate employed for ordinary foundry shapes is silica wherein at least about 70 weight percent and preferably at least about 85 weight percent of the sand is silica. Other suitable aggregate materials include zircon, olivine, aluminosilicate sand, chromite sand, and the like. Although the aggregate employed is preferably dry, it can contain minor amounts of moisture.
In molding compositions, the aggregate constitutes the major constituent and the binder constitutes a relatively minor amount. In ordinary sand type foundry applications, the amount of binder is generally no greater than about 10% by weight and frequently within the range of about 0.5% to about 7% by weight based upon the weight of the aggregate. Most often, the binder content ranges from about 0.6% to about 5% by weight based upon the weight of the aggregate in ordinary sand-type foundry shapes.
The binder compositions are preferably made available as a three-part system with the polyether polyol component as one part (Part I), and the polyisocyanate component as the other part (Part II), and the catalyst as the third part (Part III). Usually, the polyether polyol component is first mixed with sand and catalyst, and then the polyisocyanate component is added. Methods of distributing the binder on the aggregate particles are well-known to those skilled in the art.
The foundry binder system is molded into the desired shape, such as a mold or core, and cured. Curing by the no-bake process takes place by mixing a liquid amine curing catalyst into the foundry binder system, shaping it, and allowing it to cure, as described in U.S. Pat. No. 3,676,392. Useful liquid amines have a pKb value generally in the range of about 5 to about 11. Specific examples of such amines include 4-alkyl pyridines, isoquinoline, arylpyridines, 1-vinylimidazole, 1-methylimidazole, 1-methylbenzimidazole, and 1,4-thiazine. Preferably used as the liquid tertiary amine catalyst is an aliphatic tertiary amine, particularly (3-dimethylamino)propylamine. In general, the concentration of the liquid amine catalyst will range from about 0.2 to about 10.0 percent by weight of the phenolic resin, preferably 1.0 percent by weight to 4.0 percent by weight, most preferably 2.0 percent by weight to 5.0 percent by weight based upon the weight of the polyether polyol component.
The following abbreviations and components are used in the Examples:
The following abbreviations are used: